The approach of a vehicle to a station for docking requires the provision of information on distance and attitude relative to the station to facilitate docking. Instances where such information is required include backing trailer trucks to a loading dock, aircraft docking at airports, and space shuttle docking at a space station.
It is necessary to indicate both distance and attitude of a vehicle, such as a space shuttle, relative to the station during the approach. Microwave radar is useful for measuring distance at very close range but is not suitable for additionally measuring direction and relative attitude. A detection system for docking should be capable of indicating distance, azimuth and elevation. Of these components, distance can be readily measured by the use of microwave radar, but radar is not adapted for sensing the elevation and attitude of the vehicle.
Assembling a space station in sections and provisioning it prior to manning it necessitates many repeated dockings of a space vehicle with the station. The space station and vehicle are generally powered and in orbit. It is necessary to maneuver the powered vehicle to correct errors in course and range so that a soft docking of the vehicle at the space station can be made promptly. To conserve fuel, it is desirable to avoid the necessity of making difficult and prolonged computations before docking.
A lighted docking target has been utilized by the Skylab, comprising a single circular ring of lights composed of strips of the electroluminescent type. However, indication of on-axis and off-axis orientation or attitude was not provided by the target. Distance determination over a large range of distances was not provided.
U.S. Pat. No. 3,767,309 issued Oct. 23, 1973 to Brown et al discloses a guidance apparatus providing lateral and longitudinal visual guidance to the operator of the vehicle. A light projection apparatus and filter emits several multi-color, laterally disposed beam segments to provide a course guidance to the vehicle. However, no range information is provided. U.S. Pat. No. 3,910,533 issued Oct. 7, 1975 to Cheathem et al discloses a spacecraft docking and alignment system wherein a three dimensional target screen is mounted along the axis of one spacecraft and a television camera is installed along the axis of another spacecraft. The television displays the relative alignment of the two spacecrafts to the operator for docking maneuvering.
U.S. Pat. No. 3,794,270 issued Feb. 26, 1974 to Wilkens describes an apparatus for determining the relative attitude of two vehicles by using magnetic members in synchronization with each other. The attitude of a vehicle relative to an imaginary axis connecting the members is determined by sensing the orientation of a moveable magnet member relative to the vehicle in which it is mounted. The attitude and range of the vehicle cannot be determined visually, but must be obtained from a computer.
None of the above patents describe a system which visually indicates to an operator of the vehicle the range and attitude of the vehicle to assist in docking the vehicle with a station.